1. Field of the Invention
The present invention is a method of routing calls to external networks from a calling node of a private network having a plurality of external network access circuit groups.
2. Description of the Prior Art
The invention concerns private telecommunication networks. These networks are formed of communication nodes interconnected by links carrying calls and/or signaling. In such networks, some nodes have circuit groups providing access to networks outside the private network, for example for a call to a party who is not on the private network or for overflow from the private network to an external network if the private network resources are congested.
In prior art private networks a circuit group providing access to an external network is seized by routing the call from the originating user to the node providing physical access to the circuit group, from which an outgoing call is made to the external network. The access node is a fixed parameter of the circuit group: for a user connected to a given node of the private network, a circuit group is also seized in the same way. The mechanism is the same in the event of overflow to the external network.
A node of the private network has a list of overflow circuit groups, which are used in succession in the event of problems. If access to the requested circuit group is congested or unavailable, the call is returned to the originating node from the node providing physical access to that circuit group; the originating node repeats the circuit group request using the next circuit group from the list. FIG. 1 shows one example of a network operating in accordance with this principle. FIG. 1 shows a private network 1 comprising three nodes 2, 3 and 4. The nodes 3 and 4 have access circuit groups 7 and 8 to an external network 6, which can be another private network or a public network. The node 2 contains a list of circuit groups (7, 8); a list of circuit groups providing access to node 2 and to circuit group 7 is supplied in response to a circuit group seizure request from a user at node 2. The request is transmitted to node 3, as shown symbolically in the figure by the arrow 10; if the resources are not available, the request is returned to the originating node (node 2xe2x80x94arrow 11 in the figure) and the second circuit group 8 from the list is selected, as shown by the arrow 12. If that circuit group is also congested or unavailable the request is again sent back to node 2.
This solution gives rise to serious traffic problems in the event of congestion of circuit groups. It increases the external circuit group call setup time. It does not manage the resources available in the network efficiently and cannot adapt demand to suit the load on the network.
The invention proposes a solution to the above problems, manages access to external networks and the resources of the private network more efficiently and limits the traffic across the private network generated by access to the circuit groups.
The invention is a method of routing calls to an external network from a calling node of a private network having a plurality of external network access circuit groups wherein each circuit group is connected to a gateway node of the private network, which method:
calculates a cost for different possible routes to the external network, the cost of a route to the external network being a function of the circuit group used and the route in the private network between the calling node and the gateway node of the circuit group used; and
chooses a route as a function of the calculated costs.
In one embodiment of the invention the cost of a route to the external network is a decreasing function of the available resources of the circuit group used.
The cost of a route to the external network is preferably a decreasing function of the load of the links used for routing in the private network.
The cost of a route to the external network can also be a decreasing function of the number of links used for routing in the private network.
In another embodiment of the invention the step of choosing a route minimizes the cost of the route to the external network.
The method advantageously further comprises the exchange in the private network of maintenance messages between the various gateway nodes.
In this case, a maintenance message contains information on the available resources of a circuit group of a gateway node.
The step of calculating various possible routes to the external network preferably uses the Dijkstra algorithm.